Automatic power supply selector for ACPI-compliant PCI devices

Abstract

Apparatus for automatically selecting one of two or more available power supply voltages for use as a main power supply of a PCI adapter is described. In one embodiment, a power supply selector is designed such that the presence of a positive voltage at a Vaux input thereof prevents power at a Vcc input thereof from driving a main power supply input to a PCI adapter. Conversely, the absence of a positive voltage at the Vaux results in the main power supply input to the PCI adapter being derived from the Vcc input. In an alternative embodiment, jumpers are provided for enabling a user to select which power supply will be used as the “default” power supply for the adapter.

What is claimed is:  
     
       1. A method of selecting between two different voltages to be provided at an output of a power selector, the method comprising: 
       connecting a first switch means to a first power selector input;  
       connecting a second switch means between the first power selector input and a power selector output, and to the first switch means;  
       connecting a third switch means between a second power selector input and the power selector output, and to the first and second switch means, where one of the first and second power selector inputs is a main input and, the other of the first and second power selector inputs is a default input;  
       determining whether a first voltage is applied at the first power selector input;  
       if a first voltage is detected at the first power selector input, providing the first voltage at the power selector output and preventing a second voltage applied at the second power selector input from being provided at the power selector output; and  
       if a first voltage is not detected at the first power selector input, providing the second voltage applied at the second power selector input, at the power selector output.  
     
     
       2. The method of  claim 1  further comprising regulating the second voltage. 
     
     
       3. The method of  claim 1  wherein the first voltage is +5 volts and the second voltage is +3.3 volts. 
     
     
       4. The method of  claim 1  wherein the first voltage is +3.3 volts and the second voltage is +5 volts.